Silver halide emulsions containing pyrrole cyanine dyes

ABSTRACT

NOVEL CYANINE DYES WHICH FEATURE A PYRROLE NUCLEUS LINKED, BY THE 2-CARBON ATOM THEREOF, TO THE METHANE CHAIN OF THE DYE, ARE USEFUL SENSITIZERS IN PHOTOGRAPHIC SILVER HALIDE EMULSIONS.

United States Patent ice US. Cl, 96-101 29 Claims ABSTRACT OF THE DISCLOSURE Novel cyanine dyes which feature a pyrrole nucleus linked, by the 2-carbon atom thereof, to the methane chain of the dye, are useful sensitizers in photographic silver halide emulsions.

This invention relates to novel photographic materials, and more particularly to a new class of cyanine dyes, to novel photographic silver halide emulsions containing these dyes, and to new photographic elements prepared with such emulsions.

Direct positive images are known to be obtained with certain types of photographic silver halide emulsions. For example, photographic emulsions have been proposed for this purpose comprising certain cyanine dyes which function as electron acceptors, and silver halide grains that have been fogged with a combination of a reducing agent and a compound of a metal more electropositive than silver. One of the advantages of such direct positive emul sions is that the high-light areas of the images obtained with these materials are substantially free of fog. However, known materials of tis type have not exhibited the high speed required for many applications of photography. Also, such known materials have not shown the desired selective sensitivity, especially to radiation in the green to red region of the spectrum. It is evident, therefore, that there is need in the art for improved direct positive photographic materials having both good speed and desirable sensitivity to longer wavelength radiations.

It is, accordingly, an object of this invention to provide a new class of cyanine dyes that avoid the above mentioned disadvantages of prior art desensitizing dyes. Another object is to provide novel and improved photographic silver halide emulsions, such as fogged direct positive emulsions containing one or more of the new cyanine dyes of this invention. Another object is to provide such novel emulsions containing a color former. Another object is to provide novel photographic elements comprising a support having thereon at least one layer containing a novel emulsion of this invention. Another object is to provide methods for the preparation of such novel dyes and photgraphic materials of this invention. Other objects will be apparent from this disclosure and the appended claims.

We have now found that cyanine dyes derived from pyrroles containing a free 2-position carbon atom are outstanding electron acceptors and spectral sensitizers for direct positive type photographic silver halide emulsions. They provide superior reversal systems, especially with fogged silver halide emulsions that are characterized by both good speed and desired selective sensitivity to radia tion in the green to red region of the spectrum, with maximum sensitivity occurring in most cases in the region of about .540630 ITl/L. The images produced with these new direct positive photographic emulsions are clear and sharp, and of excellent contrast.

The new class of cyanine dyes of this invention include those comprising first and second 5- to 6-membered nitrogen containing nuclei joined by a methine linkage; the first of said nuclei being a pyrrole nucleus joined at the 2-carbon atom thereof to said linkage; and said second nucleus 3,592,653 Patented July 13, 1971 being of the type used in the production of cyanine dyes including both sensitizing and desensitizing nuclei joined at a carbon atom thereof to said linkage, to complete said cyanine dye.

The preferred cyanine dyes of the invention that are especially useful as electron acceptors and spectral sensitizers for direct positive photographic silver halide emulsions are represented by the following general formula:

wherein n represents a positive integer of from 1 to 2; L represents a methine linkage, e.g., CH=, C(CH C(C H etc.; R represents an alkyl group, including substituted alkyl, (preferably a lower alkyl containin gfrom 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, heXyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups (preferably a substituted lower alkyl containing from 1 to 4 carbon atoms), such as a hydroxyalkyl group, e.g., fi-hydroxyethyl, w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., ,B-methoxyethyl, wbutoxybutyl, etc., a carboxyalkyl group, e.g., B-carboxyethyl, w-carboxybutyl, etc., a sulfoalkyl group, e.g., fi-sulfoethyl, w-sulfobutyl, etc., a sulfatoalkyl group, e.g., fi-sulfatoethyl, w-sulfatobutyl, etc., an acyloxyalkyl group, e.g., fi-acetoxyethyl, 'y-acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group, e.g., fl-rnethoxycar bonylethyl, w-ethoxycarbonylbutyl, etc. or an aralkyl group, e.g., benzyl, phenethyl, etc.; an alkenyl group, e.g., allyl, l-propenyl, Z-butenyl, etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; R R R and R each represents a hydrogen atom, an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl, dodecyl, etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, nitrophenyl, etc.; X represents an acid anion, e.g., chloride, bromide, iodide, perchlorate, sulfamate, thiocyanate, p-toluenesulfonate, methyl, sulfate, etc.; and Z represents the non-metallic atoms necessary to complete a sensitizing or desensitizing nucleus containing from 5 to 6 atoms in the heterocyclic ring, which nucleus may contain a second hetero atom such as oxygen, sulfur, selenium or nitrogen, i.e., a nucleus of the type used in the production of cyanine dyes, such as the following representative nuclei:

A thiazole nucleus, e.g., thiazole, 4-methylthiazole, 4- phenylthiazole, S-methylthiazole, S-phenylthiazole, 4,5- dimethylthiazole, 4,5 diphenylthiazole, 4-(2-thienyl) thiazole, benzothiazole, 4-chlorobenzothiazole, 4- or 5- nitrobenzothiazole, 5-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, S-methylbenzothiazole, 6-methylbenzothiazole, 6-nitrobenzothiazole, S-bromobenzothiazole, 6-bromobenzothiazole, 5chloro-6-nitrobenzothiazole, 4-phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole, S-iodobenzothiazole, 6 iodobenzothiazole, 4 ethoxybenzothiazole, 5 ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6 dimethoxybenzothiazole, 5,6 dioxymethylenebenzothiazole, 5 hydroxybenzothiazole, 6 hydroxybenzothiazole, oz naphthothiazole, 13 naphthothiazole, 5,5 naphthothiazole, 5 methoxy 5,5- naphthothiazole, 5-ethoXy-B-naphthothiazole, 8-methoXy-a-naphthothiazole, 7methoXy-a-naphthothiazole, 4'-methoxythianaphtheno 7,6',4,5 thiazole, nitro group substituted naphthothiazoles, etc.;

an oxazole nucleus, e.g., 4-methyloxazole, 4-nitro-oxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole,

4-ethyloxazole, 4,5-dimethoxazole, S-phenyloxazole, benzoxazole, 5 chlorobenzoxazole, 5 methylbenzoxazole, 5 phenylbenzoxazole, 5- or 5 nitrobenzoxazole, 5 chloro 6 nitrobenzoxazole, 6 methylbenzoxazole, 5,6 dimethylbenzoxazole, 4,6 dimethylbenzoxazole, 5 methoxybenzoxazole, 5 ethoxybenzoxazole, 5 chlorobenzoxazole, 6 methoxybenzoxazole, 5 hydroxybenzoxazole, 6 hydroxybenzoxazole, u-naphthoxazole, fi-naphthoxazole, nitro group substituted naphthoxazoles, etc.;

a selenazole nucleus, e.g., 4-methylselenazole, 4-nitroselenazole, 4-phenylselenazole, benzoselenazole, 5-chlorobenzoselenazole, 5-methoxybenzoselenazole, 5-hydroxybenzoselenazole, 5- or 6-nitrobenzoselenazole, 5- chloro 6-nitrobenzoselenazole, tetrahydrobenzoselenazole, a-naphthoselenazole, B-naphthoselenazole, nitro group substituted naphthoselenazoles, etc.;

a thiazoline nucleus, e.g., thiazoline, 4-methylthiazoline,

4-nitrothiazoline, etc.;

a pyridine nucleus, e.g., Z-pyridine, S-methyl-Z-pyridine, 4-pyridine, 3-methyl-4-pyridine, nitro group substituted pyridines, etc.;

a quinoline nucleus, e.g., Z-quinoline, B-methyl-Z-quinoline, S-ethyI-Z-quinoline, 6-chloro-2-quinoline, 6-nitro- 2-quinoline, 8-chloro-2-quinoline, 6-methoxy-2-quinoline, 8-ethoxy-2-quinoline, 8-hydroxy-2-quinoline, 4- quinoline, 6-methoxy-4-quinoline, 6-nitro-4-quinoline, 7-methyl-4-quinoline, 8-chloro-4-quinoline, l-isoquinoline, 3-isoquinoline, etc.;

6-nitro-1-isoquinoline, 3,4-dihydro-l-isoquinoline,

a 3,3-dialkylindolenine nucleus, preferably having a nitro or cyano substitutent, e.g., 3,3-dimethyl-5- or 6-nitroindolenine, 3,3-dimethyl-5- or 6-cyanoindolenine, etc.; and,

an imidazole nucleus e.g., imidazole, l-alkylimidazole, 1-

alkyl-4-phenylimidazole, 1-alkyl-4,S-dimethylimidazole, benzimidazole, l-alkylbenzimidazole, l-alkyl-S-nitrobenzimidazole, 1-aryl-5,6-dichlorobenzimidazole, 1- alkyl-a-naphthimidazole, 1-aryl-fl-naphthimidaz0le, 1- alkyl-S-methOXy-a-naphthimidazole, or,

an imidazo[4,5-b]quinoxaline nucleus, e.g, 1,3-dialkylimidazo[4,5-b]quinoxaline such as 1,3-diethylimidazo- [4,5-b1quinoxaline, 6-chloro-1,3-diethylimidazo[4,5-b] quinoxaline, etc., 1,3-dialkenylimidazo[4,5-b]quinoxaline such as 1,3-diallylimidazo[4,5-b]quinoxaline, 6- chloro-1,3-diallylimidazo[4,5-b]quinoxaline, etc., 1,3- diarylimidazo[4,5-b]quinoxaline such as 1,3-diphenylimidazo[4,5-b1quinoxaline, 6-chloro 1,3-diphenylimidazo[4,5-b]quinoxaline, etc.;

a 3,3-dialkyl-3H-pyrrolo[2,3-b1pyridine nucleus e.g., 3,3- dimethyl-3H-pyrrolo[2,3-b]pyridine, 3,3 diethyl-3H- pyrrolo[2,3-b]pyridine, etc.;

a thiazolo[4,5-b]quinoline nucleus; and the like.

Nuclei wherein Z completes an imidazo[4,5-b]quinoxaline nucleus, or a nitro group substituted thiazole, oxazole, selenazole, thiazoline, pyridine, quinoline, indole, or imidazole nucleus are desensitizing nuclei. Dyes of the invention produced with these densensitizing nuclei are particularly efficacious, and in the instances wherein the pyrrole nucleus contains phenyl group substituents at the 1- and 5-positions of the pyrrole ring, they are outstanding electron acceptors and spectral sensitizers, and are the preferred dyes species of the invention.

The novel cyanine dyes of the invention defined above are powerful electron acceptors and spectral sensitizers for direct positive photographic silver halide emulsions. In addition, they are also useful desensitizers in emulsions used in the process described in Steward and Reeves, U.S. Pat. No. 3,250,618, issued May 10, 1966.

As used herein desensitizing nucleus refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 0.2 gram dye per mole of silver, cause by electron trapping at least about an percent loss in the blue speed of the emulsion when sensitometrically exposed and developed three minutes in Kodak developer D-19 at room temperature. Advantageously, the densitizing nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described, essentially completely densensitize the test emulsion to blue radiation (i.e., cause more than about to loss of speed to blue radiation).

The cyanine dyes defined by Formula I above are conveniently prepared, for example, by reacting at from 15 C. to refluxing temperatures a mixture of (1) a heterocyclic compound of the formula:

wherein 11, R X and Z are previously defined, and R represents methyl, ethyl, benzyl, etc., and (2) a pyrrole compound of the formula:

wherein R R R and R are as previously defined, in approximately equimolar proportions, in the presence or absence, as desired, of a condensing agent such as a trialkylamine, e.g., triethylamine, etc., piperidine N-methylpiperidine, etc., in an inert solvent medium such as an alkanol, e.g., ethanol, or acetic anhydride. Chain-substituted dyes are prepared when R represents ethyl, benzyl etc., The crude dyes are then separated from the reaction mixtures and purified by one or more recrystallizations from appropriate solvents such as methanol, mixtures of dimethylacetamide and methanol, and the like.

The intermediate compounds of Formula III above are conveniently prepared, for example, by reacting a mixture of approximately equimolar amounts of (1) a compound of the formula:

wherein R R R and R are as previously defined, and (2) an N,N-dimethylformamide/phosph0ryl chloride complex, in an inert solvent medium such as dichloroethane. Preferably (2) is agitated with the dichloroethane and the pyrrole compound (1) is slowly added thereto in the form of a solution thereof in dichloroethane at the temperature of an ice bath. The mixture is then heated to reflux for a short period, cooled and an aqueous solution of sodium acetate is then added. After further refluxing, the crude product is separated by appropriate decantation and extraction methods and recrystallized from a suitable solvent such as ligroin.

In accordance with the invention, novel and improved direct positive photographic silver halide emulsions are prepared by incorporating one or more of the cyanine dyes of the invention into a suitable fogged silver halide emulsion. The emulsion can be fogged in any suitable manner, such as by light or with chemical fogging agents, e.g., stannous chloride, formaldehyde, thiourea dioxide, and the like. The emulsion may be fogged by the addition thereto of a reducing agent, such as thiourea dioxide, and a compound of a metal more electropositive than silver, such as a gold salt, for example, potassium chloroaurate, as described in British Pat. 723,019 (1955).

Typical reducing agents that are useful in providing such emulsions include stannous salts, e.g., stannous chloride, hydrazine, sulfur compounds such as thiourea dioxide, phosphonium salts such as tetra(hydroxymethyl) phosphonium chloride, and the like. Typical useful metal compounds that are more electropositive than silver include gold, rhodium, platinum, palladium, iridium, etc., preferably in the form of soluble salts thereof, e.g., potassium chloroaurate, auric chloride, (NH PdCl and the like.

Useful concentrations of reducing agent and metal compound (e.g., metal salt) can be varied over a considerable range. As a general guideline, good results are obtained using about .05 to 40 mg. reducing agent per mole of silver halide and 0.5 to 15.0 mg. metal compound per mole of silver halide. Best results are obtained at lower concentration levels of both reducing agent and metal compound.

The concentration of added dye can vary widely, e.g., from about 50 to 2000 mg. and preferably from about 400 to 800 mg. per mole of silver halide in the direct positive emulsions.

As used herein, and in the appended claims, fogged refers to emulsions containing silver halide grains which produce a density of at least 0.5 when developed, with out exposure, for 5 minutes at 68 F. in developer Kodak DK-50 having the composition set forth below, when the emulsion is coated at a silver coverage of 50 mg. to 500 mg. per square foot.

DEVELOPER G. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite (anhydrous) 30.0 Hydroquinone 2.5 Sodium metaborate 10.0 Potassium bromide 0.5

Water to make 1.0 liter.

The dyes of this invention are also advantageously incorporated in direct positive emulsions of the type in which a silver halide grain has a water-insoluble silver salt center and an outer shell composed of a fogged water-insoluble silver salt that develops to silver without exposure. The dyes of the invention are incorporated, preferably, in the outer shell of such emulsions. These emulsions can be prepared in various ways, such as those described in Berriman U.S. patent application Ser. No. 448,467, filed Apr. 15, 1965, now U.S. Pat. 3,367,778 issued Feb. 6, 1968. For example, the shell of the grains in such emulsions may be prepared by precipitating over the core grains a light-sensitive water-insoluble silver salt that can be fogged and which fog is removable by bleaching. The shell is of sufficient thickness to prevent access of the developer used in processing the emulsions of the invention to the core. The silver salt shell is surface fogged to make it developable to metallic silver with conventional surface image developing compositions. The silver salt of the shell is sufiiciently fogged to produce a density of at least about 0.5 when developed for 6 minutes at 68 F. in Developer A below when the emulsion is coated at a silver coverage of 100 mg. per square foot. Such fogging can be effected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core emulsion, high intensity light and the like fogging means well known to those skilled in the art. While the core need not be sensitized to fog, the shell is fogged. Fogging by means of a reduction sensitizer, a noble metal salt such as gold salt plus a reduction sensitizer, a sulfur sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized. The shell portion of the subject grains can also be coated prior to fogging.

DEVELOPER A G. N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0 Potassium metaborate 35.0 Potassium bromide 1.0

Water to 1 liter. pH of 9.6.

Before the shell of water-insoluble silver salt is added to the silver salt core, the core emulsion is first chemically or physically treated by methods previously described in the prior art to produce centers which promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can be obtained by various techniques as described herein. Chemical sensitization techniques of the type described by Antoine Hautot and Henri Sauvenier in Science et Industries Photographiques, vol. XXVIII, January 1957, pages 1 to 23 and January 1957, pages 57 to 65 are particularly useful. Such chemical sensitization includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization, such as by a labile sulfur compound, and reduction sensitizati on, e.g., treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.

The dyes of this invention are highly useful electron acceptors in high speed direct positive emulsions comprising fogged silver halide grains and a compound which accepts electrons, as described and claimed in Illingsworth U.S. patent application Ser. No. 619,936, filed Mar. 2, 1967, now U.S. Pat. 3,501,307, issued Mar. 17, 1970, and titled Photographic Reversal Materials Case C. The fogged silver halide grains of such emulsions are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about one upon processing for six minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for six minutes at about 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide 50 mg. Acetic acid (glacial) 3.47 cc. Sodium acetate 11.49 g. Potassium bromide 119 mg. Water to 1 liter.

The grains of such emulsions will lose at least about 25% and generally at least about 40% of their fog when bleached for ten minutes at 68 F. in a potassium cyanide bleach composition as described herein. This fog loss can be illustrated by coating the silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 upon processing for six minutes at about 68 F. in Kodak DK-50 developer and comparing the density of such a coating with an identical coating which is processed for six minutes at 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at 68 F. in the potassium cyanide bleach composition. As already indicated, the maximum density of the unbleached coating will be at least 30% greater, generally at least 60% greater, than the maximum density of the bleached coating.

The silver halides employed in the preparation of the photographic emulsions useful herein include any of the photographic silver halides as eX-amplified by silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide, and the like. Silver halide grains having an average grain size less than about one micron, preferably less than about 0.5 micron, give particularly good results. The silver halide gains can be regular and can be any suitable shape such as cubic or octahedral, as described and claimed in Illingsworth U.S. Patent application Ser. No. 619,909, filed Mar. 2, 1967, now U.S. Patent 3,501,306, issued Mar. 17, 1970, and titled Direct Positive Photographic Emulsions Case A. Such grains advantageously have a rather uniform diameter frequency distribution, as described and claimed in Illingsworth US. Pat. application Ser. No. 619,948, filed Mar. 2, 1967, now US. Pat. 3,501,305 issued Mar. 17, 1970, and titled Photographic Reversal Emulsions Case B. For example, at least 95%, by weight, of the photographic silver halide grains can have a diameter which is within about 40%, preferably within about 30% of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., as shown in an article by Trivelli and Smith entitled Empirical Relations Between Sensitometric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, vol. LXXIX, 1949, pp. 330-338. The fogged silver halide grains in these direct-positive photographic emulsions of this invention produce a density of at least 0.5 when developed without exposure for five minutes at 68 F. in Kodak DK50 developer when such an emulsion is coated at a coverage of 50 to about 500 mg. of silver per square foot of support. The preferred photographic silver halide emulsions comprise at least 50 mole percent bromide, the most preferred emulsions being silver bromoiodide emulsions, particularly those containing less than about ten mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

In the preparation of the above photographic emulsions, the dyes of the invention are advantageously incorporated in the washed, finished silver halide emulsion and should, of course, be uniformly distributed throughout the emulsion. The methods of incorporating dyes and other addenda in emulsions are relatively simple and well known to those skilled in the art of emulsion making. For example, it is convenient to add them from solutions in appropriate solvents, in which case the solvent selected should be completely free from any deleterious effect on the ultimate light-sensitive materials. Methanol, isopropanol, pyridine, water, etc., alone or in admixtures, have proven satisfactory as solvents for this purpose. The type of silver halide emulsions that can be sensitized with the new dyes include any of those prepared with hydrophilic colloids that are known to be satisfactory for dispersing silver halides, for example, emulsions comprising natural materials such gelatin, albumin, agar-agar, gum arabic, alginic acid, etc. and hydrophilic synthetic resins such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose ethers partially hydrolyzed cellulose acetate, and the like.

The binding agents for the emulsion layer of the photographic elcment can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in US. Patents 3,142,568; 3,193,386; 3,062,674

and 3,220,844 and include the water insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The dyes, reducing agents and metal compounds of the invention can be used with emulsions prepared, as indicated above, with any of the light-sensitive silver halide salts including silver chloride, silver bromide, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide, etc. Particularly useful are direct positive fogged emulsions in which the silver salt is a silver bromohalide comprising more than 50 mole percent bromide. Certain dyes of this invention are also useful in emulsions which contain color formers.

The novel emulsions of this invention may be coated on any suitable photographic support, such as glass, film base such as cellulose acetate, cellulose acetate butyrate, polyesters such as poly(etl1ylene terephthalate), paper baryta coated paper, polyolefin coated paper, e.g., polyethylene or polypropylene coated paper, which may be electron bombarded to promote emulsion adhesion, to produce the novel photographic elements of the invention.

The invention is further illustrated by the following examples.

8 EXAMPLE 1 3-ethyl-6-nitro-2-[2-( 2-pyrrolyl)vinyl] benzothiazo lium p-toluenesulfonate 3-ethyl-2-methyl-6-nitrobenzothiazolium p-toluene-sulfonate (7.9 g., .02 mole), pyrrole-2-carboxaldehyde (1.9 g., .02 mole) and piperidine (3 drops) are dissolved in ethanol (25 ml.) and heated at reflux with stirring, for 5 minutes. After chilling, the solid is collected on a filter, rinsed with ethanol and dried. The yield of crude dye is 5.9 g. (78%) and, after one recrystallization from methanol, the yield of purified dye is 3.5 g. (46%), MP. 254 255 C., decomposes.

The above prepared dye containing the desensitizing 3-ethyl-6-nitrobenzothiazole nucleus is photographically tested for its usefulness as an electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions by the following procedure.

A gelatin silver bromoiodide emulsion (2.5 mole percent of the halide being iodide) and having an average grain size of about 0.2 micron is prepared by adding an aqueous solution of potassium bromide and potassium iodide, and an aqueous solution of silver nitrate, simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 C., over a period of about minutes. The emulsion is chill-set, shredded and washed by leaching with cold water in the conventional manner. The emulsion is reduction-gold fogged by first adding 0.2 mg. of thiourea dioxide per mole of silver and heating for minutes at C. and then adding 4.0 mg. of potassium chloroaurate per mole of silver and heating for 60 minutes at 65 C. The dye of the above example, 3-ethyl-6-nitro-2- [2 (2 pyrrolyl)-vinyl]benzothiazolium p-toluenesulfonate, is then added to the above fogged emulsion in amount sulficient to give the concentration recorded in Table I hereinafter of the dye per mole of silver. The resulting emulsion is coated on a cellulose acetate film support at a coverage of mg. of silver and 400 mg. of gelatin per square foot of support.

A sample of the coated support is then exposed on an Easman lb sensitometer using a tungsten light source and processed for 6 minutes at room temperature in Kodak D-19 developer which has the folowing composition:

G. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite (anhydrous) 90.0 Hydroquinone 8.0 Sodium carbonate (monohydrate) 52.5 Potassium bromide 5.0

Water to make 1.0 liter.

then fixed, washed and dried. The results are listed in Table I hereinafter. Referring thereto, it will be seen that the dye of this example has a maximum density in the unexposed areas of 1.90 and a minimum density in exposed areas of 0.66, a maximum sensitivity of 585 nm. and a relative speed of 479. In contrast, the control containing no dye shows a speed of less than 1, and exhibits no reversal. These results indicate that the dye compound of the above example is well suited to function as both an electron acceptor and spectral sensitizer for fogged direct positive silver halide emulsions. It thus provides good quality direct positive photographic silver halide emulsions. Excellent magenta images are obtained when the color former 1-(2,4,6-trichlorophenyl)-3,3'-(2,4"-dit-pentylphenoxyacetamido)benzamido 5 pyrazolone is incorporated in the emulsion of this example, the emulsion is coated on a support, exposed to a tungsten source through Wratten filter No. 61 and No. 16, and reversal processed as described in Graham et al. US. Pat. 3,046,- 129, issued July 24, 1962, in Example (a) col. 27, lines 27 et seq. except that black-and-white (MQ) development is omitted, the color development is reduced to one minute and is conducted in total darkness until after fixing.

EXAMPLE 2 1,3,3-trimethyl-5 -nitro-2-[2-(2-pyrrolyl)vinyl]- 3H-indolium p-toluenesulfonate 1,2,3,3 tetramethyl 5 nitro 3H indolium ptoluenesulfonate (3.9 g., .01 mole) and pyrrole-2-carboxaldehyde (0.95 g., .01 mole) are stirred With ethanol (15 ml.) at room temperature for 10 minutes. Seed crystals, obtained from a test tube experiment are then added and the mixture is allowed to stir for an additional 35 minutes. The solid is collected on a filter and dried. The crude yield is 4.0 g. (85%) and, after one recrystallization from methanol, the yield of purified dye is 1.5 g. (32%), M.P. 253-254 C. d.

This dye containing the desensitizing 1,3,3-trimethyl- 5-nitro-3H-indole nucleus is photographically tested by the exact procedure described in above Example 1. The results are recorded in Table 1 hereinafter. Referring to the table, it will be noted that the densities are 1.74 and 0.12 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 570 nm. and a relative speed of 832. Accordingly, this dye is a good quality electron acceptor and spectral sensitizer for fogged direct positive silver halide emulsions.

EXAMPLE 3 3-ethyl-2- 2-( 1-methy1-2-pyrrolyl) vinyl] -6-nitrobenzothiazolium p-toluenesulfonate 3 ethyl 2 methyl 6 nitrobenzothiazolium p toluenesulfonate (3.9 g., .01 mole), l-methylpyrrole-Z- carboxaldehyde (1.1 g., .01 mole) and piperidine (3 drops) are dissolved in ethanol ml.) and heated at reflux, with stirring, for 3 minutes. After chilling, the solid is collected on a filter, washed sparingly in a beaker with ethanol, collected again and dried. The yield of crude dye is 2.4 g. (49%) and, after one crystallization from methanol, the yield of purified dye is 1.5 g. (31%), M.P. 256-257 C., d.

This dye containing the desensitizing 3-ethyl-6-nitro benzothiazole nucleus is tested by the exact procedure of above Example 1 and found, as shown in Table l hereinafter, to be an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions. The densities are shown to be 1.46 and 0.05 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 585 nm. and a relative speed of 912.

OgN-

EXAMPLE 4 1, 3 3 -trimethyl-2- [2-( 1-methyl-2-pyrrolyl)vinyl] -5- nitro-SH-indolium iodide on, I e

' 1,2,3,3 tetramethyl 5 nitro-3H-indolium .p-toluenesulfonate (3.9 g., .01 mole), 1-methylpyrrole-2-carboxaldehyde (1.1 g., .01 mole) and piperidine (3 drops) are dissolved in ethanol (15 ml.) and heated at reflux, with stirring, for 3 minutes. After chilling, the solid is collected on a filter, washed sparingly in a beaker with ethanol, collected again and dried. The solid (2.2 g.) is then dissolved in methanol (10 ml.) and an aqueous solution of sodium iodide (2.0 g.) added. After chilling, the solid is collected on a filter and recrystallized from methanol. The yield of purified dye is 0.8 'g. (18%), M.P. 340 C.

The above prepared dye containing the desensitizing 1, 3,3-trimethyl-5-nitro-3H-indole nucleus is tested by the exact procedure described in above Example 1. The results in Table 1 hereinafter show densities of 1.47 and 0.08 in the unexposed and exposed areas, respectively, with maximum sensitivity at 570 nm. and a relative speed of 692, thereby indicating the dye of the above example is an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions.

EXAMPLE 5 3-ethyl-2- 2- 5 -methyl-2-pyrrolyl vinyl -6-nitrobenzothiazolium p-toluenesulfonate o H: o1-r \M o H \N/ 3 l 111 5-methylpyrr0le-2-carboxaldehyde (1.1 g., 0.1 mole) 3 ethyl-2-methyl-6-nitrobenzothiazolium p-toluenesulfonate (4.0 g., .01 mole) and piperidine (3 drops) are dissolved in ethanol (15 ml.) and the mixture heated with stirring. Solid separates before refluxing temperature is reached and additional ethanol (10 ml.) is added. The mixture is then heated at reflux for 5 minutes. After chilling, the crude dye is collected on a filter, rinsed with ethanol and dried. The crude yield is 3.6 g. (74%) and, after one recrystallization from methanol, the yield of purified dye is 2.4 g. (49%), M.P. 277-278" C., d.

The photographic testing of the above prepared dye containing the 3-ethyl-6-nitro-2-benzothiazole nucleus is carried out by the exact procedure described in above Example 1. The results, as shown in Table 1 hereinafter, of maximum densities of 1.56 and 0.07 in the unexposed and exposed areas, respectively, with maximum sensitivity at 605 nm. and a relative speed of 631, indicate that the dye of the above example is an excellent electron acceptor and spectral sensitizer for fogged photographic reversal emulsions.

EXAMPLE 6 3-ethyl-6-nitro-2- 2- 1-phenyl-2-pyrrolyl vinyl] benzothiazolium perchlorate 1-phenylpyrrole-2-carboxaldehyde (1.7 g., .01 mole) and 3-ethyl-2-methyl 6 nitrobenzothiazolium p-toluenesulfonate (3.9 g., .01 mole) are dissolved in ethanol (20 ml.) and heated at reflux, with stirring, for 5 minutes. An aqueous solution of sodium perchlorate (1.5 g.) is then added and after chilling, the crude dye is collected on a filter washed in a beaker with ethanol, collected again and dried. The crude yield is 4.6 g. (96%) and, after one recrystallization from N,N-dimethylacetamide/ methanol, the yield of purified dye is 2.1 g. (44%), M.P. 2s1-2s2 (3., d.

The photographic testing of the above prepared dye containing the 3-ethyl-6-nitro-2-benzothiazole nucleus is carried out by the exact procedure described in above Example 1. The results, as shown in Table 1 hereinafter, of maximum densities of 1.28 and 0.02 in the unexposed and exposed areas, respectively, with maximum sensitivity at 555 nm. and a relative speed of 1380, indicate that the dye of the above example is an exceptionally useful electron acceptor and spectral sensitizer for fogged photographic reversal emulsions.

EXAMPLE 7 1,3-diethyl-2- 2-( l-phenyl-2-pyrrolyl)vinyl]imidazo- [4,5-b] quinoxalinium perchlorate 1 ,3-diethyl-2-niethylimidazo [4,5 -b quinoxalinium p-toluenesulfonate (4.1 g., .01 mole) are dissolved and 1-phenylpyrrole-2-carboxaldehyde (1.7 g., .01 mole) are dissolved in acetic anhydride (1-5 ml.) and heated at refiux, with stirring, for 1 minute. After cooling ether (200 ml.) is added. After decanting, the residue is dissolved in a minimum of boiling ethanol and the ethanol solution is treated with an aqueous solution of sodium perchlorate (1.5 g.). After chilling, the solid is collected on a filter and recrystallized from methanol. The yield of purified dye is 1.2 g. (25%), MP. 280-281 C., d.

This dye containing the desensitizing 1,3-diethylimidazo]4,5-b]quinoxaline nucleus is tested by the exact procedure of above Example 1 and found, as shown in Table 1 hereinafter, to be an exceptionally useful electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions. The densities are shown to be 1.50 and 0.04 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 545 nm. and a relative speed of 1290.

EXAMPLE 8 1,3,3-trimethyl--nitro-2-[2-(1-nitrophenyl-2-pyrrolyl) vinyl]-3H-indolium p-toluenesulfonate l-(p-nitrophenyl)-2-pyrrolecarboxaldehyde 1.1 g., .005 mole) and 1,2,3,3-tetrarnethyl-5-nitro-3H-indolium p-toluenesulfonate (2.0 g. .005 mole) are dissolved in acetic anhydride ml.) and heated at reflux, with stirring, for 1% minutes. After chilling, the solid is collected on a filter, rinsed with acetone and dried. The crude yield is 2.2 g. (76%) and, after one recrystallization from methanol, the yield of purified dye is 1.5 g. (52%), MP. 248-249 C., d.

The above prepared dye containing the desensitizing 1,3,3-trimethyl-5-nitro-3H-indole nucleus is photographically tested by the procedure described in above Example 1. The results are recorded in Table 1 hereinafter. Referring thereto, the densities are 1:57 and 0.08 for the unexposed and exposed areas, respectively, with a maximum 12 sensitivity at 575 nm. and a relative speed of 1150. Accordingly, this dye is an exceptionally useful electron acceptor and spectral sensitizer for fogged direct positive silver halide emulsions.

EXAMPLE 9 l,3-diethyl-2-[2-(1-p-nitrophenyl-2-pyrrolyl)vinyl] imidazo[4,5-b] quinoxalinium iodide 1 (p-nitrophenyl) 2 pyrrolecarboxaldehyde (1.1 g., .005 mole) and 1,3 diethyl 2 methylimidazo[4,5-b] quinoxalinium p-toluenesulfonate (2.1 g., .005 mole) are dissolved in acetic anhydride (15 ml.) and heated at reflux, with stirring, for 1% minutes. After chilling, the solid is collected on a filter and rinsed with acetone. The filtrate is terated with ether (300 ml.) and, after decanting, a sticky residue is obtained. The solid and sticky residue are combined and disolved in warm ethanol. The ethanol solution is treated with an aqueous solution of sodium iodide (1.0 g.) and, after chilling, the solid is collected on a filter. After one recrystallization from ethanol, the yield of purified dye is 0.3 g. (11%), MP. 236-237" C., d.

This dye containing the desensitizing 1,3-diethyl-imidazo[4,5-b]quinoxaline nucleus is tested by the exact procedure of above Example 1 and is indicated by the values in Table 1 hereinafter, it is an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions. The desities are shown to be 1.17 and 0.05 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 550 nm. and a relative speed of 1260.

The following Examples 10, 11 and 12 illustrate the remarkable extension of spectral sensitivity and increase in relative speed when the pyrrole nucleus is substituted at both the 1-position and the 5-position of the pyrrole ring.

EXAMPLE 10 2-[2-(1,5-diphenyl-2-pyrrolyl)vinyl]-3-ethyl-6-nitrobenzothiazolium perchlorate 1,5 diphenylpyrrole 2 carboxaldehyde (1.2 g., .005 mole) and 3 ethyl 2 methyl 6 nitrobenzothiazolium p-toluenesulfonate (2.0 g., .005 mole) are dissolved in ethanol (15 m1.) and heated at reflux, with stirring, for 5 min. A hot aqueous solution of sodium perchlorate (1.0 g./ 10 ml.) is added and a solid percipitated. After chilling, the crude dye is collected on a filter and recrystallize from N,N dimethylacetamide/methanol. The yield is 1.4 g. (50%), MP. 254255 C., dec.

The photographic testing of the above prepared dye containing the 3-ethyl-6-nitro-2-benzothiazole nucleus is carried out by the exact procedure described in above Example 1. The results, as shown in Table 1 hereinafter, of maximum densities of 1.30 and 0.06 in the unexposed and exposed areas, respectively, with maximum sensitivity at 610 nm. and a relative speed of 1780, indicate that the dye of the above example is an outstanding electron acceptor and spectral sensitizer for fogged photographic reversal emulsions.

EXAMPLE 11 2-[2-(1,5-diphenyl-2-pyrrolyl)vinyl]-1,3,3-trimethyl-5- nitro-3H-indolium perchlorate HaC CH3 1,5 diphenylpyrrole 2 carboxaldehyde (1.2 g., .005 mole) and 1,2,3,4 tetramethyl nitro 3H indolium p toluenesulfonate (2.0 g., .005 mole) are dissolved in ethanol (15 ml.) and heated at reflux, with stirring, for 5 min. A hot aqueous solution of sodium perchlorate (1.0 g./ 10 ml.) is then added and a solid precipitated. After chilling, the crude dye is collected on a filter and recrystallize from N,N-dimethylacetamide/methanol. The yield is 1.5 g. (56%), MP. 273-274 C., dec.

This dye containing the desensitizing 1,3,3-trimethyl- 5-nitro-3H-indole nucleus is tested by the procedure described in above Example 1. The results are recorded in Tabel 1 hereinafter. Referring thereto, the densities are 1.64 and 0.06 for the unexposed and exposed areas, respectively, with maximum sensitivity at 625 nm. and a relative speed of 2400. These results indicate that this dye is an outstanding electron acceptor and spectral sensitizer for fogged direct positive silver halide emulsions.

EXAMPLE 12 2- [2- 1,5-diphenyl-2-pyrrolyl vinyl] 1 ,3 -diethylimidazo [4,5 -b] -quinoxalinium perchlorate 1,5-diphenylpyrrole-2-carboxaldehyde (2.5 g., .01 mole) and 1,3-diethyl-2methylimidazo[4,5-b]quinoxalinium ptoluene sulfonate (4.1 g., .01 mole) are dissolved in acetic anhydride (15 ml.) and heated at reflux, with stirring, for 2 minutes. After cooling, 175 ml. are added with stirring. The ether is then decanted, the residue dissolved in a minimum of boiling ethanol, and then a hot aqueous solution of sodium perchlorate (1.5 g./ 10 ml.) is added. After chilling, the solid is collected on a filter and recrystallized from N,N-dimethylacetamide/ methanol. The yield is 2.7 g. (47%), MP. 293-294 C., dec.

This dye containing the desensitizing 1,3-diethylimidazo [4,5-b1quinoxaline nucleus is tested by the exact procedure of above Example 1 and, as shown by the values in Table 1 hereinafter, it is an outstanding electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions. The densities are 1.72 and 0.05 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 600 nm. and a relative speed of 1590.

The effectiveness of the new cyanine dyes of the invention as electron acceptors and spectral sensitizers, as indicated by the testing procedure described in above Example 1, is summarized in the following table.

TAB LE 1 Density Conc. dye, Relative Max. un- Min. Maximum g./mol clear exposed exposed sensitivity silver speed areas areas (nm.)

0.00 1 1. 90 No reversal It will be apparent from the foregoing that other cyanine dyes of this invention having generally similar electron acceptor and spectral sensitizing properties may be prepared by appropriate selection of intermediates defined by Formulas II and III above. Typical other dye compounds wherein Z of Formula I above completes a desensitizing nucleus includes, for example, the dye 3- ethyl 2 [2-(1-methyl-2-pyrrolyl)vinyl]-6-nitrobenzoxazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts), the dye 3-ethyl-2-[2- (1 methyl 2 pyrrolyl)vinyl]-6-nitrobenzoselenazolium salt (e.g., the chloride, bromide, iodide, perchlorate, ptoluenesulfonate, etc. salts), the dye 3-ethyl-6-nitro-2-[2- (l-phenyl-Z-pyrrolyl)vinyl]benzoxazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts), the dye 3-ethyl-6-nitro-2-[2-(l-phenyl-Z-pyrrolyl)vinyl]benzoselenazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salt), 3 phenyl-6-nitro-2-[2-(l-phenyl-Z-pyrrolyl)vinyl]benzothiazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts), the dye 1,3-diallyl 2- 2- l-phenyl-Z-pyrrolyl vinyl] imidazo [4,5 -b quinoxazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesul'fonate, etc. salts), the dye 1,3-diphenyl 2 [2-(1-phenyl-2-pyrrolyl)vinyl]imidazo[4,5-b] quinoxazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts), the dye 2-[2- (1,5 diphenyl 2-pyrrolyl)'vinyl]-1,3-diallylimidazo[4,5- b]quinoxazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts), the dye 2-[2- (1,5 diphenyl 2 pyrrolyl)vinyl]-1,3-diphenylimidazo [4,5-b]quinoxazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts) and the like dyes.

"Still other highly useful cyanine dyes of the invention wherein Z of Formula I above completes a sensitizing nucleus includes, for example, the dye 3-ethyl-2-[2-(lmethyl-2-pyrrolyl)vinyl]benzothiazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts), the dye 3-ethyl-2-[2-(1-methyl-2-pyrrolyl) vinyl]benzoxazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts), the dye 3-ethyl-2- [2- l-methyI-Z-pyrrolyl vinyl] benzoselenazolium salt (e.g., the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc. salts) and the like dyes.

The following examples illustrate the preparation of a number of the pyrrole intermediates employed in the preparation of the new cyanine dyes of the invention.

EXAMPLE 13 2-methylpyrrole This compound is prepared in the manner described by Cantor, et al., J. Org. Chem., 21, 918 (1956).

EXAMPLE l4 5-methylpyrrole-2carboxaldehyde In a 500 ml. 3-neck flask equipped with a reflux condenser, thermometer, stirring device, and a dropping funnel is placed N,N-dimethylformamide (19.0 g., 0.26 mole). After cooling to C., POCl (40 g., 0.26 mole) is added, with stirring, over the course of minutes with the temperature kept between 1020 C. The mixture is then allowed to stir at room temperature for 15 minutes and then dichloroethane (60 ml.) is added. After cooling to 5 C., a solution of 2-methylpyrrole (17.5 g., 0.22 mole) in dichloroethane (60 ml.) is added over a period of 1 hour, with stirring, at the temperature of an ice bath. The mixture is then heated at reflux for 15 minutes. After cooling to -30 C., a solution of sodium acetate (100 g., 1.2 moles) in water (200 ml.) is added cautiously at first; and then as rapidly as possible with vigorous stirring. The mixture is then refluxed for 15 minutes with vigorous stirring. After cooling, the dichlorethane layer (top) is removed and the aqueous layer is extracted with ether (50 ml./3 The ether extracts and dichloroethane layer are combined and washed with 20 ml. portions of saturated aqueous sodium carbonate until CO ceased to evolve. The ether-dichloroethane mixture is dried over sodium carbonate and, after evaporations of the solvents under reduced pressure, the solid is obtained. After two recrystallizations from ligroin (B.P. -60 C.), the yield of purified 5-methylpyrrole-2- carboxaldehyde is 11 g. (46%), MP. 6870 C.

EXAMPLE 15 l-phenylpyrrole This compound is prepared in the manner described by Elming and Caluson-Kaas, Acta. Chemica Scandinavica, 6, 867-874 (1952).

EXAMPLE 16 l-phenylpyrrole-Z-carboxaldehyde This compound is prepared in the manner described in Example 14, except that l-phenylpyrrole is employed in place of Z-methylpyrrole.

EXAMPLE 17 1- p-nitrophenyl -2-pyrrolecarboxaldehyde This compound is prepared in the manner described in CA, 47:8005d (1953).

1 6 EXAMPLE 18 1,2-diphenylpyrr0le Call;

This compound is prepared in the manner described by Treibs and Dena, Ann., 589, 176.

EXAMPLE 19 l,5-diphenylpyrrole-2-carboxaldehyde This compound is prepared in the manner described in Example 14, except that 1,2-diphenylpyrrole is employed in place of 2-methylpyrrole.

The following examples further illustrate the preparation of fogged, direct positive photographic emulsions and elements with the cyanine dyes of the invention.

EXAMPLE 20 To 9.0 pounds of a silver chloride gelatin emulsion containing an equivalent of grams of silver nitrate is added 0.017 gram of 3-ethy1-2-[2-(l-methyl-Z-pyrrolyl) vinyl] 6 nitrobenzothiazolium p toluenesulfonate (Example 3). The emulsion is coated on a non-glossy paper support, and is flashed with white light to give a density of 1.2 when developed in the following developer, diluted 1 part to 2 parts of water:

N-methyl-p-aminophenol sulfate 3.1 Sodium sulfite, des 45 Hydroquinone 12 Sodium carbonate, des 67.5 Potassium bromide 1.9

Water to 1 liter.

The light fogged material can be exposed to an image with light modulated by a Wratten No. 15 filter to give a direct positive image. Generally similar results are obtained when the dyes of Examples 6, 7, 8 and 9 are used in place of the above dye.

EXAMPLE 21 Seven pounds of a silver chloride gelatin emulsion containing the equivalent of 100 g. of silver nitrate is heated to 40 C. and the pH is adjusted to 7.8. Eight cc. of full strength (40%) formalin solution is added and the emulsion is held at 40 C. for 10 minutes. At the end of the holding period, the pH is adjusted to 6.0 and 0.125 g. of 2-[2-(1,S-diphenyl-Z-pyrrolyl)vinyl] 3 ethyl 6 nitrobenzothiazolium perchlorate is added (Example 10). The emulsion is coated on a support, and provides good direct positive images. Similar results are obtained when the dyes of Examples 11 and 12 are substituted for the above dye.

By substituting other dye compounds of the invention, as defined in Formula I above, into the procedure of the above examples, similar fogged, direct positive photographic silver halide emulsions and photographic elements may be prepared.

The photographic silver halide emulsion and other layers present in the photographic elements made according to the invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde, and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxy starch or oxy plant gums, and the like. The emulsion layers can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, absorbing dyes, plasticizers, and the like. These photographic emulsions can also contain in some cases additional spectral sensitizing dyes. Furthermore, these emulsions can contain color forming couplers or can be developed in solutions containing couplers or other color generating materials. Among the useful color formers are the monomeric and polymeric color formers, e.g., pyrazolone color formers, as well as phenolic, heterocyclic and open chain couplers having a reactive methylene group. The color forming couplers can be incorporated into the direct positive photographic silver halide emulsion using any suitable technique, e.g., techniques of the type shown in Jelley et al. U.S. Pat. 2,322,027, issued June 15, 1943, Fierke et a]. U.S. Pat. 2,801,171, issued July 30, 1957, Fisher U.S. Pats. 1,055,155 and 1,102,028 issued Mar. 4 1913 and June 30, 1914, respectively, and Wilmanns U.S. Pat. 2,186,849 issued Jan. 9, 1940. They can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. A fogged direct positive photographic silver halide emulsion containing at least one cyanine dye selected from those comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined by a dimethine linkage; the first of said nuclei being a pyrrole nucleus joined at the 2-carbon atom thereof to said linkage; and, said second nucleus being a desensitizing nucleus.

2. A direct positive emulsion in accordance with claim 1 wherein said cyanine dye contains a nitro substituted desensitizing nucleus.

3. A direct positive emulsion in accordance with claim 1 wherein said cyanine dye contains an imidazo[4,5-b] quinoxaline desensitizing nucleus.

4. A direct positive emulsion in accordance with claim 1 in which the said silver halide is present in the form of chemically fogged silver halide grains.

5. A direct positive emulsion in accordance with claim 1 in which the said silver halide is present in the form of reduction and gold fogged silver halide grains.

6. A direct positive emulsion in accordance with claim 1 containing a photographic color former.

7. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver emulsion on a support to give a miximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-SO developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide 50 mg.

Acetic acid (glacial) 3.47 cc.

Sodium acetate 11.49 g.

Potassium bromide 119 mg.

Water to 1 liter.

8. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, at least 95%, by weight, of said grains having a diameter which is Within about 40% of the mean grain diameter.

9. A fogged direct positive photographic silver halide emulsion containing at least one cyanine dye selected from those represented by the following general formula:

wherein n represents a positive integer of from 1 to 2; L represents a methine linkage; R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group; R R R and R each represents a member selected from the group consisting of a hydrogen atom, an alkyl group, and an aryl group; X represents an acid anion; and Z represents the non-metallic atoms required to complete a 5- to 6-membered nitrogen containing desensitizing nucleus.

10. A direct positive emulsion in accordance with claim 9 wherein said Z represents the non-metallic atoms required to complete a nitrobenzothiazole nucleus.

11. A direct positive emulsion in accordance with claim 9 wherein said Z represents the non-metallic atoms required to complete a nitrobenzoxazole nucleus.

12. A direct positive emulsion in accordance with claim 9 wherein said Z represents the non-metallic atoms required to complete a nitrobenzoselenazole nucleus.

13. A direct positive emulsion in accordance with claim 9 wherein said Z represents the non-metallic atoms required to complete an imidazo[4,5-b]quinoxaline nucleus.

14. A direct positive emulsion in accordance with claim 9 wherein said Z represents the non-metallic atoms required to complete a 3,3-dialkyl-3H-nitroindole nucleus.

15. A direct positive emulsion in accordance with claim 9 in which the said silver halide is present in the form of chemically fogged silver halide grains.

16. A direct positive emulsion in accordance with claim 9 in which the said silver halide is present in the form of reduction and gold fogged silver halide grains.

17. A direct positive emulsion in accordance with claim 9 containing a photographic color former.

18. A direct positive photographic emulsion in accordance with claim 9 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide 50 mg.

Acetic acid (glacial) 3.47 cc.

Sodium acetate 11.49 g.

Potassium bromide 119 mg.

Water to 1 liter.

19. A direct positive photographic emulsion in accordance with claim 9 which comprises fogged silver halide grains, at least by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

20. A direct positive emulsion in accordance with claim 9 containing a cyanine dye selected from the group consisting of:

3-ethyl-6-nitro-2- [2- (2-pyrrolyl) vinyl] benzothiazolium salt 1,3,3-trimethyl-5-nitro-2- [2- (2-pyrrolyl) vinyl] -3H- indolium salt 3-ethyl-2- [2- 1-methyl-2-pyrrolyl) vinyl] -6-nitrobenzothiazolium salt 1,3 ,3-trimethy1-2- [2-( l-methyl-Z-pyrrolyl) vinyl] -5- nitro-3H-indolium salt 3-ethyl-2- [2- 5-methyl-2-pyrrolyl) vinyl] -6-nitrobenzothiazolium salt 3-ethyl-6-nitro-2- [2-( l-phenyl-Z-pyrrolyl vinyl] benzothiazolium salt I 9 1,3-diethyl-2- 2- l-phenyl-Z-pyrrolyl vinyl] imidazo- [4,5-b] quinoxalinium salt 1,3,3 -trimethyl--nitro-2- [2- l-p-nitrophenyl-Z-pyrrolyl)vinyl] -3H-indolium salt 1,3-diethyl-2-[2-(1-p-nitrophenyl-2-pyrrolyl)vinyl] imidazo [4,5-b quinoxalinium salt 2- 2-( 1,5 -diphenyl-2-pyrrolyl vinyl] 3-ethyl-6-nitrobenzothiazolium salt 2-[2-(1,5-diphenyl-2-pyrrolyl)vinyl]-l,3,3-trirnethyl- 5-nitro-3H-indolium salt 2- [2- 1,5-diphenyl-2-pyrrolyl vinyl] 1 ,3-diethylimidazo [4,5 -b] quinoxalim'um salt 21. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 1.

22. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 7.

23. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 8.

24. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 9.

25. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 18.

26. A photographic element comprising a support having at least one layer containing a direct positive emulsion of claim 19.

27. A photographic silver halide emulsion containing as desensitizer a cyanine dye comprising first and second 5- t0 6-membered nitrogen containing heterocyclic nuclei joined by a dimethine linkage; the first of said nuclei being a pyrrole nucleus joined at the Z-carbon atom thereof to said linkage; and said second nucleus being a desensitizing nucleus.

28. A photographic silver halide emulsion containing as desensitizer a cyanine dye represented by the following wherein n represents a positive integer of from 1 to 2; L represents a methine linkage; R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group; R R R and R each represents a member selected from the group consisting of a hydrogen atom, an alkyl group, and an aryl group; X represents an acid anion; and Z represents the nonmetallic atoms required to complete a 5- to 6-membered nitrogen containing desensitizing nucleus.

29. A photographic silver halide emulsion containing as desensitizer a cyanine dye selected from the group consisting of:

3-ethyl- 6-nitro-2- [2- 2-pyrrolyl) vinyl] benzothiazolium salt 1,3,3-trimethyl-5-nitro-2- [2- (2-pyrrolyl vinyl] -3H- indolium salt 3-ethyl-2- [2- l-methyl-Z-pyrrolyl) vinyl] -6-nitro benzothiazolium salt 1,3,3-trimethyl-2-[2-(1-methyl-2-pyrrolyl)vinyl-5- nitro-3H-indolium salt 3-ethy1-2-[2-(S-methyl-Z-pyrrolyl)vinyl]-6-nitrobenzothiazolium salt 3 -ethy1-6-nitro-2- 2-( l-phenyl-2-pyrrolyl vinyl] 'benzothiazolium salt 1,3-diethyl-2- [2- l-phenyl-Z-pyrrolyl) vinyl] imidazo- [4,5-b] quinoxaliniurn salt 1,3,3-trimethy1-5-nitro-2- [2-( l-p-nitrophenyl-Z-pyrrolyl)vinyl]-3H-indolium salt 1,3-diethyl-2- [2-( 1-p-nitrophenyl-2-pyrrolyl vinyl] imidazo[4,5-b1quinoxalinium salt 2- [2-( 1,5-diphenyl-2-pyrrolyl vinyl] -3 -ethyl-6-nitro benzothiazoliuln salt 2- [2-( 1,5-diphenyl-2-pyrrolyl vinyl] l ,3,3-trimethyl- 5-nitro-3H-indolium salt 2- [2- 1,5-diphenyl-2-pyrrolyl) vinyl] 1 ,3-diethylimidazo [4,5-b1quinoxalinium salt References Cited UNITED STATES PATENTS 2,466,523 4/1949 White et al 96-102 2,481,674 9/1949 Knott et al 96-105 2,503,775 4/1950 Sprague 96-106 2,719,151 4/1955 Haseltine et a1. 96-102 2,882,160 4/1959 De Stevens 96-105 J. TRAVIS BROWN, Primary Examiner US. Cl. X.R. 96-130; 260-240 

